Over the years, brachytherapy sources implanted into the human body have become a very effective tool in radiation therapy for treating diseased tissues, especially cancerous tissues. The brachytherapy sources are also known as radioactive seeds in the industry. Typically, these radioactive seeds are inserted directly into the tissues to be irradiated using surgical methods or minimally invasive techniques such as hypodermic needles. These radioactive seeds typically contain a radioactive material such as iodine-125 which emits low energy X-rays to irradiate and destroy malignant tissues without causing excessive damage to the surrounding healthy tissue, as disclosed by Lawrence in U.S. Pat. No. 3,351,049 ('049 patent). Because radioactive materials like iodine-125 have a short half-life and emit low energy X-rays, the radioactive seeds can be left in human tissue indefinitely without the need for surgical removal. However, although radioactive seeds do not have to be removed from the embedded tissues, it is necessary to determine the position and the number of radioactive seeds implanted in a patient's tissue to effectively treat the patient. This information is also useful in computing the radiation dosage distribution in the tissue being treated so that effective treatment can be administered.
In the '049 patent, the radioactive seed includes a therapeutic amount of radioisotope appropriately distributed on a carrier body. The carrier body is sealed inside an elongated cavity of a capsule to prevent the radioisotope from interacting with body fluids while at the same time permitting the radiation to pass through the walls of the capsule. Furthermore, to allow X-ray detection of the radioactive seed, the radioactive seed contains an X-ray marker made of a dense, high atomic number material, such as gold, which can block the transmission of X-rays so that the radioactive seed can be detected by using X-ray photographic techniques. The capsule, which is typically made out of a low atomic number material, cannot be detected using X-ray photographic techniques because low atomic number materials allow X-rays and radiation to pass through them, instead of blocking X-rays and radiation.
The '049 patent discloses two methods of providing an X-ray marker. In one method, a small ball constructed of a dense, high atomic number material, such as gold or tungsten, is provided in between two cylindrical carrier bodies impregnated with a radioisotope. In another method, a wire made of a high atomic number dense material is located along the central axis of symmetry of the carrier body that is impregnated with a radioisotope. Both the X-ray marker and the carrier body are encapsulated and sealed within a low atomic numbered material container or a capsule which minimally absorbs the radiation emitted by the radioisotope.
Although the above-described methods of providing an X-ray marker are effective in detecting the radioactive seed, they have certain problems. In the first method in which a small ball is provided as a X-ray marker, the ball just appears as a circular dot on an X-ray film and does not provide any information as to the orientation of the radioactive seed. Since the orientation of the radioactive seed is not known, the radiation dosage distribution cannot be computed accurately. In the second method in which a centrally located wire is provided as an X-ray marker, the orientation of the radioactive seed can be determined. However, the second method presents manufacturing problems, such as positioning the wire centrally at the axis of symmetry, which can raise the cost of manufacturing the radioactive seeds.
In other radioactive seeds such as one disclosed by Kubiatowicz in U.S. Pat. No. 4,323,055 ('055 patent), a long cylindrical rod-like member located centrally within the seed is usually employed as an X-ray marker. In the '055 patent, a silver rod coated with iodine-125 is employed as an X-ray marker. Although such X-ray markers like the silver rod in the '055 patent may disclose the orientation of the seed, the silver rod in the '055 patent is coated with the iodine-125 by performing a complicated chemical process which in turn will complicate the overall manufacturing process and raise the cost of manufacturing. As discussed above, the orientation of the seed can be very important in computing the radiation dosage distribution. Therefore, simpler and more cost effective apparatuses and methods are needed in providing X-ray markers which will disclose the orientation of the radioactive seed when the seed is exposed to X-ray photography.